Phosphoroamidothioate granules and methods of manufacture thereof

ABSTRACT

A method of producing a granule containing at least 40 weight percent phosphoroamidothioate, preferably acephate, by processing the phosphoroamidothioate in powder form along with a liquid through a vertical continuous noncompressive agglomerator having a vertical rotating shaft on which are mounted a plurality of adjustable blades.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Patent App. Ser.No. 60/801,775 filed May 19, 2006, the entire contents of which areincorporated herein by reference.

FIELD OF THE INVENTION

The invention relates to insecticidally active phosphoroamidothioategranules and methods of manufacture thereof.

BACKGROUND OF THE INVENTION

As used hereinafter and in the claims, phosphoroamidothioate meansphosphoroamidothioate and phosphoroamidodithioate. Certainphosphoroamidothioates are known in the art as having excellentinsecticidal activity against a variety of insects. A particularlyimportant commercial insecticide within this class of compounds is theinsecticide acephate (generic name) or Orthene® (trade name), which canbe systemically taken up by a plant so that insects which feed and/orlive on the plant are killed, in addition to those insects whichdirectly ingest or are contacted by the insecticide. Acephate andrelated compounds are described in U.S. Pat. Nos. 3,716,600, 3,845,172and 3,914,417, which disclose that in addition to their insecticidalproperties, the compounds possess very low mammalian toxicity. Ortheneis commercially produced as a technical grade chemical of about 97 to99.5% purity (typically about 98%), which is often referred to asacephate technical or acephate TG (technical grade).

Acephate technical is commercially available as a powder, which has atendency to clump or agglomerate. In the past, acephate technical hasbeen applied to crops as a dust (for example, after exposure to moisturevia rain, dew or irrigation), or in spray form as a water solutionspray. Dusts are undesirable because of airborne contamination andhandling difficulties, while liquid spray formulations involve solventand packaging expenses, and container disposal requirements that detractfrom commercial desirability.

In recent years, suggestions have been made to providephosphoroamidothioates in a pellet form or other type of granule.Phosphoroamidothioate-containing pellets and granules have been proposedin U.S. Pat. Nos. 5,075,058, 5,100,667, 5,464,623, 5,298,501, 5,352,674,5,369,100, 6,013,272, 6,337,323, 6,761,897, 6,875,381, and 6,752,943;the entire contents and disclosures of each of these patents is herebyincorporated herein by reference. Pellets and other granules have theadvantages of eliminating dust problems and reducing offensive odors incomparison to powder forms because of a reduced surface area to weightratio. However, there is a need for an improved process to produceimproved granules, the improved process being more productive with lesscost to produce improved granules.

SUMMARY OF THE INVENTION

A method of producing a granule containing phosphoroamidothioatecomprising the steps of providing phosphoroamidothioate in powder formalong with a liquid to a noncompressive agglomerator and processing saidpowder and said liquid through said agglomerator to yield a granulewhich is, on a dry basis, at least 40 weight percentphosphoroamidothioate. A granule produced by the method is alsoprovided.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective, cut-away view of a vertical continuousnoncompressive agglomerator useful in the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

As used herein, when a range, such as 5 to 25 (or 5-25) is given, thismeans preferably at least 5 and, separately and independently,preferably not more than 25. Unless otherwise indicated or apparent,percents are weight percents. Unless otherwise indicated, meshes andscreen sizes are U.S. Standard size.

With reference to FIG. 1 there is shown a continuous, in-line verticalgravity flow noncompressive agglomerator 10 useful in the presentinvention. Agglomerator 10 includes housing 40 and an electric motor 12which spins (in a counterclockwise direction when viewed from the top) acentral vertical free hanging rotating shaft 22 on which are mounted twobladeholders 42 on each one of which are mounted a plurality ofadjustable blades 24; each blade 24 being adjustable through 360° byrotating its circular baseholder 44. Preferably the shaft 22 is fittedwith 2 or 3 bladeholders 42 with preferably 6 blades on each holderarranged symmetrically as shown. The shaft 22 has a long bearing supportclear of the product stream. In operation, fines or powders 20 (whichcan comprise one or more different powders) are provided to theagglomerator 10 through an inlet channel 30 as shown via arrows 32. Asthe powders 20 are fed through the top of the agglomerator 10 and passthrough by gravity in a continuous stream, liquids are injected viaspray nozzles on liquid injectors 14 placed around the top of thevertical cylindrical mixing chamber 26. 1, 2, 3, 4, or more liquidinjectors 14 to inject one or more liquids of the same or differentviscosities can be placed evenly and concentrically around the top orupper portion of the cylindrical mixing chamber 26. The liquid spray isgenerally atomized using compressed air. The powder 20 and liquid sprayare turbulently mixed in chamber 26 (which is preferably 160-400, suchas 160, 250, 335 or 400, mm in diameter) by the rapidly spinning orrotating adjustable blades 24 and spiral downward as shown by arrows 34,36. Discrete agglomerated granules 28 drop out the bottom of the unit.The short retention time in chamber 26 (less than 2 seconds or less than1 second) make high production rates possible. Control over particlesize, density, and dispersibility can be accomplished by adjusting rotorspeed (1000-3500 RPM), rotor element (blade angle) pitch, feed rate, andbinder/solid ratio. As can be seen, the agglomerator 10 operates in acontinuous, non-batch manner and agglomerates in a noncompressivemanner, that is, it does not use compressive force to compress orextrude the powder material into granules or pellets. An extruderoperates in a compressive manner and uses compressive force to extrudethe material into pellets.

Agglomerator 10 preferably has a continuously deforming mixing chamber26 which is surrounded by a cylindrical flexible neoprene or elastomericsidewall 16 which is continuously deformed and massaged by a pluralityof pneumatically operated sidewall rollers 18 which are moved verticallyalong the outside of the sidewall 16 via pneumatic translation apparatus38. This helps avoid material buildup by keeping wetted particles fromadhering to the chamber wall although a slight layer of product remainson the inner wall preventing excessive wear of the neoprene. In additionto reducing clogging, this action helps inhibit particulateover-densification while yielding a more uniform particle with moreconsistent density, cohesiveness and solubility. Alternatively and lesspreferably agglomerator 10 can be provided with a rigid metal sidewall16 and without sidewall rollers 18.

Agglomerator 10 is preferably K-G/Schugi Blender-AgglomeratorFlex-O-Mix, such as Model Nos. 160, 250, 335, or 400, manufactured bySchugi B.V., Amsterdam, The Netherlands and distributed by K-G Divisionof Bepex Corporation, Rosemont, Ill., less preferably the correspondingSchugimix machine (with rigid sidewall) from the same manufacturer anddistributor; the foregoing machines are noncompressive agglomerators.These machines are known in the agglomerator art.

Preferred formulations for the invented granules, on a dry basis, are asfollows.

INGREDIENTS (by weight percent) More preferred More preferred Preferredwt. % wt. % wt. % Phosphoroamidothioate, 40-100 90-99 94-95 preferablyacephate or 60-100 91-98 95-99 acephate TG 80-100 92-97 96-99 85-10093-96 97-99 Filler or Inert Filler 0-60  0-15 4-7 0-40  1-10 5-6 0-202-9 3-8 Binding Agent 0-10 2-8 5-6 0.1-5   2-9 6-7 1-9  3-8 7-8 1-3  4-7

The phosphoroamidothioate used is preferably acephate, which isavailable as acephate TG. Acephate TG is commercially available and isabout 98 wt. % pure. The filler or inert filler is preferably zeolite orclay or other fillers known in the art, preferably water dispersible,which are preferably added as dry powders. The binding agent is optionaland is added to make the granules stronger and harder.

If a binding agent is desired, the filler can be reduced by the amountof binding agent added. The binding agent can be starch or Agrimer orpotassium sulfate or other binding agents known in the art; Agrimer(polyvinylpyrrolidone) can be Agrimer VA6 (vinyl pyrrolidone/vinylacetate copolymer) or similar. Starch and Agrimer are preferably addedas dry powders; potassium sulfate is preferably added as part of thewater. The weight percent of (a) filler and (b) binding agent in the dryformulation can be 0 or can be preferably at least, or not more than, 1,2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, or 15, weight percent. Thefillers and binding agents can be soluble or non soluble in water. Apreferred formulation which is about 90 wt. % acephate is about 92 wt. %acephate TG, 6 wt. % zeolite or other filler, and 2 wt. % starch orother binding agent (alternatively, the starch or binding agent can be0-4 wt. % and the zeolite can be 4-8 wt. %, with the acephate TGremaining at about 92 wt. %). Another preferred formulation is 98.5 wt.% acephate TG and 1.5 wt. % binder such as starch, potassium sulfate,Agrimer or other binding agent. Another preferred formulation is 100%acephate TG, which has a natural clumping ability. Another preferredformulation which is about 75 wt. % acephate is about 76.5 wt. %acephate TG, 21.5 wt. % filler and 2 wt. % binding agent. Any otherformulations between the formulations given can also be used. Granuleswith at least or about 80, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, and98 weight % active ingredient (preferably acephate) are preferred inmany cases. For example, to produce finished granules with a target of90% active ingredient, the pre-mix would contain about 91.8% acephate TG(assuming 98% purity) and 8.2% inert filler and/or binding agent. Theinvented granules preferably do not have any other ingredients thanthose mentioned herein.

A preferred process to make the invented granules is as follows. The rawmaterials are received in bulk containers. The dry ingredients arepre-mixed and blended according to the formulation desired in aconventional paddle mixer or ribbon blender such as from Marion Mixers.The pre-mix of dry ingredients passes through a hammer mill, such asfrom Fitzpatrick Corp., in order to de-lump and provide a uniform mix.The dry pre-mix is then fed to a continuous flow agglomerator(preferably agglomerator 10, through inlet channel 30) at apre-determined or metered rate and mixed with water to form granules.Water is preferably added such that the granules exiting the chamber 26are about 3-6 wt. % water.

If desired, a binding agent may be added in liquid form along with waterthrough liquid injectors 14. With reference to FIG. 1, the pre-mix isadded through inlet channel 30, water and optionally other liquids areadded through liquid injectors 14, the ingredients are turbulentlycombined and agglomerated into granules in chamber 26 via whirlingblades 24 and drop out the bottom as agglomerated granules 28. Granules28 preferably exit into a fluid bed dryer such as from Carrier Corp.where the granules are dried preferably to less than 1% moisture to formspheroidal agglomerates. As can be seen, granules 28 are not extruded.

Granules exiting the fluid bed dryer are screened to size; the oversized particles (which are retained on a screen size of about 6 or 8 or10 mesh (U.S. Standard size)) are ground in a hammer mill and returnedto the inlet of the screener. Fines, or under sized particles (whichpass through a screen size of about 60 or 80 or 100 mesh (U.S. Standardsize)) are recycled and blended into the virgin powder feed stream to beagglomerated. The process yields a dry flow, dust free, watersoluble/dispersible granule having a diameter of preferably about0.15-3.5, more preferably about 0.25-2.4, more preferably about 0.5-2,mm and a bulk density (loose) of preferably 29-37 or 30-36 or 31-35 or32-34 or about 33, lbs/cubic foot and a bulk density (tapped) ofpreferably 32-40 or 33-39 or 34-38 or 35-37 or about 36, lbs/cubic foot.

The invented granules preferably are more porous and sponge-like thanthe hard, compacted extruded pellets produced according to U.S. Pat.Nos. 6,752,943, 6,875,381, 6,013,272, 6,337,323 and 6761897, such thatthe invented granules will disperse and dissolve faster in water. Theinvented granules preferably have a dissolution rate in water of about9-15 or 10-14 or 11-13 or about 12, inversions (fill a 100 ml graduatedcylinder with 100 ml of water, then add 1 g of sample and then stopperthe cylinder, then invert the cylinder for the first inversion andpermit the sample to settle to the bottom, then repeat these inversionsuntil the sample has dissolved) and an attrition rate of about 0.01-5 or0.01-3 or 0.01-2 or 0.1-1 or 0.2-0.9 or 0.3-0.8 or 0.4-0.7 or 0.5-0.6 orabout 0.54, percent. Attrition is measured by obtaining 50 g of a samplewhich passes through a 10 mesh screen and is retained on a 40 meshscreen (−10+40), placing the 50 g sample in a Vanderkamp Friabilator for100 revolutions, removing the sample and placing it on a 60 mesh screen,and calculating the percent that passes through the 60 mesh screen(−60). For example, if 0.4 g of the 50 g sample passes through the 60mesh screen, the attrition rate is 0.8%.

While the invention has been described with reference to preferredembodiments, it will be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted forelements thereof without departing from the scope of the invention. Inaddition, many modifications may be made to adapt a particular situationor material to the teachings of the invention without departing from theessential scope thereof. Therefore, it is intended that the inventionnot be limited to the particular embodiment disclosed as the best modecontemplated for carrying out this invention, but that the inventionwill include all embodiments falling within the scope of the appendedclaims.

1. A granule comprising, on a dry basis, at least 88 weight percentacephate, said granule being produced by a method comprising the stepsof providing acephate in powder form along with a liquid to anoncompressive agglomerator and processing said powder and said liquidthrough said agglomerator to yield a granule, said agglomerator having arotatable vertical shaft with a plurality of blades mounted to theshaft, wherein said granule has a diameter of 0.15-3.5 mm and a tappedbulk density of 32-40 lbs/cubic foot, said granule being less than 1%moisture and having a dissolution rate in water of not more than 15inversions, said inversions being counted by filling a 100 mL graduatedcylinder with 100 mL of water, adding 1 g of said granules, stopperingthe cylinder, then inverting the cylinder for the first inversion andpermitting the granules to settle to the bottom, then repeating theseinversions until the granules have dissolved.
 2. The granule of claim 1,said granule being, on a dry basis, at least 90 weight percent acephate.3. The granule of claim 1, said granule being, on a dry basis, at least95 weight percent acephate.
 4. The granule of claim 1, said granulebeing, on a dry basis, 0.1-8 weight percent binding agent.
 5. Thegranule of claim 1, wherein said liquid comprises water.
 6. The granuleof claim 1, wherein the blades are adjustable.
 7. The granule of claim4, wherein said binding agent is selected from the group consisting ofstarch, polyvinylpyrrolidone, vinyl pyrrolidone/vinyl acetate copolymer,and potassium sulfate.
 8. The granule of claim 1, said granule being, ona dry basis, 1-15 weight percent filler.
 9. The granule of claim 1,wherein said granule has a diameter of 0.25-2.4 mm.
 10. The granule ofclaim 1, wherein said granule has a tapped bulk density of 33-39lbs/cubic foot.
 11. The granule of claim 1, said granule having adissolution rate in water of not more than 14 inversions, saidinversions being counted by filling a 100 mL graduated cylinder with 100mL of water, adding 1 g of said granules, stoppering the cylinder, theninverting the cylinder for the first inversion and permitting thegranules to settle to the bottom, then repeating these inversions untilthe granules have dissolved.
 12. The granule of claim 1, wherein saidagglomerator is a continuous agglomerator.
 13. The granule of claim 1,wherein said agglomerator has a mixing chamber surrounded by a flexiblesidewall which is continuously deformed during operation.
 14. Thegranule of claim 1, wherein said granule has an attrition rate of about0.01-5 percent.
 15. The granule of claim 1, wherein, during processing,the vertical shaft rotates at a speed of 1000-3500 RPM.
 16. The granuleof claim 1, wherein said powder and said liquid is processed throughsaid agglomerator in a retention time of less than 2 seconds.
 17. Thegranule of claim 1, said granule being, on a dry basis, at least 97weight percent acephate.
 18. The granule of claim 1, said granule being,on a dry basis, at least 98 weight percent acephate.
 19. The granule ofclaim 1, wherein said granule has a diameter of 0.5-2 mm.
 20. Thegranule of claim 1, wherein said granule has a loose bulk density of29-37 lbs/cubic foot.